The long term objective of this proposal is to understand how signal transduction pathways operate, specifically, the regulation of signal transduction by scaffold proteins. The specific aims of this research proposal are to: (I). examine the distribution of MUPP1 (multi-PDZ domain protein 1), in the central nervous system by indirect immunofluorescence. (II) investigate the interaction and localization of MUPP1, with components involved in the serotonin 5-HT2C receptor-mediated pathway in the rat brain; (III) evaluate if MUPP1 PDZ domains of highest homology to INAD interact with the three INAD-interacting proteins from Drosophila. This work hopes to contribute to the growing consensus that cells are not merely cytoplasmic bags of molecules that randomly collide and allow various intracellular events to occur. On the contrary, cells tightly organize and regulate various protein:protein interaction events which lead to efficient signal transduction processes. This view of highly regulated cellular organization will increase the number of targets available for drugs to intervene and disrupt the processes of carcinogenesis, neurodegenerative diseases, as well as countless other human afflictions. Indirect immunofluorescence using the confocal microscopy will be employed (aim I). Biochemical techniques including immunoprecipitation, ligand overlay assays, and affinity chromatography will be utilized to investigate protein:protein interaction (aim II, III. Disruption of the mapped sites of interaction on MUPP1 by mutagenesis and reintroduction of these modified constructs of MUPP1 into a 5-HT2C expressing cell line will be used to evaluate the functional consequence the interaction.